1. Field of the Invention
This invention relates to a metal vapor laser device.
2. Description of the Prior Art
A metal vapor laser device generates laser oscillations making use of vapor of a working metal which is enclosed in a laser tube together with a carrier gas.
An exemplary one of metal vapor laser devices which are practically used at present is a so-called positive column type metal vapor laser device which generates laser oscillations making use of a positive column portion of a discharge. More particularly, a positive column type He-Cd laser device is known wherein helium is used as a carrier gas and cadmium is used as a working metal.
Such a He-Cd laser device can continuously oscillate, for example, an ultraviolet ray having a wavelength of 325 nm as well as visible ray having a wavelength of 442 nm in a short wavelength zone. Due to the characteristic, the demand for such He-Cd lasers has increased in recent years, and He-Cd laser devices are used in various fields as light sources, for example, for laser printers, holography, photo-plotters, color scanners and so on.
In a metal vapor laser device, when metal vapor is condensed on an inner wall of a laser tube, helium gas is trapped in the condensed metal so that the pressure of the helium gas in the laser tube decreases. Consequently, an output laser beam is liable to become unstable.
In order to prevent this, a helium gas supplier is conventionally connected to the metal vapor laser tube to supply helium gas suitably into the metal vapor laser tube.
An exemplary one of such conventional helium gas suppliers includes an outer tube substantially impermeable to helium gas, a partition having a helium gas permeability which varies according to temperature and partitioning the inside of the outer tube into a tank section and a reservoir section which communicates with the inside of a laser tube, and a heater for controlling the temperature of the partition. The temperature of the partition is thus regulated by the heater to control the permeability of the partition to helium gas.
The helium gas supplier of such a construction described just above, however, has a drawback that, since the heater is disposed on an outer periphery only of a portion of the outer tube near the partition, when the pressure within the metal laser tube is changed by a sudden change of the ambient temperature, it takes a considerable time until the pressure is restored to the original level as a result of supplement of helium gas into the metal vapor laser tube, and after all, the response of the helium gas supplier is so slow that it cannot respond sufficiently rapidly to a change of the pressure and consequently the output laser power thereof becomes unstable: